<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<script>
var a = "a";
window.b = "window.b";
c = "c";

alert(delete window.a);
alert(delete window.b);
alert(delete window.c);

alert(window.a); 
alert(window.b); 
alert(window.c); 

</script>
</head>
<body>
</body>
</html>